1. Field of the Invention
The present invention relates to a method of controlling the temperature of a susceptor for supporting a substrate to be processed in a process chamber of a processing apparatus and, for example, to a method of controlling the temperature of a susceptor in a plasma etching apparatus for a semiconductor wafer.
2. Description of the Related Art
In a technique of processing an object to be processed using a reactive gas plasma, e.g., in a dry etching technique of performing etching, there is known a method in which a wafer to be processed is etched while being cooled to obtain etching anisotropy and a high selection ratio. For example, the following low-temperature etching method is disclosed in Published Unexamined Japanese Patent Application No. 60-158627. That is, a wafer is placed on an electrode having a refrigerant reservoir to decrease the temperature of the reaction surface, thereby suppressing the side etching reaction.
In the low-temperature etching, it is important to keep the temperature of the reaction surface of a wafer within an allowable processing temperature range so as to increase the production yield and perform microprocessing on the surface. However, in a conventional plasma etching apparatus, 40 to 50% of RF power applied to generate a plasma are converted into heat energy, and the conversion efficiency to heat energy is not constant due to various factors. For this reason, it is difficult to control the wafer temperature correctly.
In a plasma etching apparatus, a large amount of a refrigerant, e.g., liquid nitrogen, is required in order to achieve a desired ultra low temperature atmosphere. In addition, a long period of time is required to achieve the ultra low temperature atmosphere. For example, about 100 minutes are required to cool a susceptor from room temperature to -140.degree. C.
Especially, when substrates to be processed of a plurality of lots are continuously processed, a large heat loss occurs every time a lot is loaded/unloaded, and temperature adjustment must be performed every time a heavy loss occurs. For this reason, a heat energy loss from the susceptor is large, thereby prolonging the processing time.
In addition, since the interior of the process chamber of the apparatus is exposed to various process gases and a plasma in a vacuum atmosphere, and is very sensitive to contamination, maintenance must be performed as needed. However, when the process chamber is opened for the maintenance, and the susceptor set in a low-temperature state is abruptly exposed to the atmospheric air, moisture contained in the atmospheric air is brought into contact with the susceptor set in the low-temperature state to often cause condensation, and the apparatus may then break down depending on conditions.
The following time-sharing etching method (intermittent etching method) is disclosed in Published Unexamined Japanese Patent Application No. 3-134187. That is, when an RF power supply is turned on to generate a plasma, and the wafer temperature is increased to a predetermined temperature range or more, etching is stopped. When the wafer temperature drops, the RF power supply is operated again, thereby controlling the wafer temperature within the predetermined temperature range. According to this intermittent etching method, while the RF power supply is set in an OFF state to control the wafer temperature, except for a case wherein the RF power supply must be turned off for processing steps, a time loss occurs, thereby decreasing the throughput. For example, assuming that the duty ratio in 1-minute etching is 50%, the processing time is doubled, i.e., becomes 2 minutes.
In Published Unexamined Japanese Patent Application No. 4-196528, the following etching apparatus is disclosed. That is, a thermoresistive member for decreasing cooling power from a cooling unit is arranged on the heat transfer path to a susceptor, and the temperature of heat generated by the thermoresistive member is controlled, thereby controlling the wafer temperature. However, the heat transfer path of the etching apparatus is complicated and long, and satisfactory wafer temperature control cannot be performed.